A conventional industrial baking oven is typically provided with a double door on the front end thereof so that the entire part of the interior of the oven may be made accessible by opening this door, and works such as LCD panels, integrated circuit boards, and semiconductor substrates may be charged into and discharged from the oven through this door. However, every time the door is opened, a substantial drop occurs in the temperature of the interior of the oven, and it means a substantial loss of energy. Furthermore, such changes in the temperature could adversely affect the baking process.